1. Field of the Invention
The present invention relates to a dielectric porcelain composition mainly containing BaO.multidot.Nd.sub.2 O.sub.3.multidot.TiO.sub.2 having a sintering property at low temperature, enabling to use Ag, Cu or an alloy containing a main component of Ag or Cu as an internal conductor.
2. Description of the Related Art
Recently, mobile communication technologies such as car telephones, cellular phone and the like have been considerably developing. In the mobile communication, high frequency zone called as quasi microwaves of several hundred MHz to several GHz. Therefore, high frequency characteristics are made great account of also in electronic devices as resonators, filters or capacitors to be used in the mobile communication instruments. Concerning the recent popularization of the mobile communication, miniaturization and low price of the communicating instruments are important factors in addition to improvement of services. Accordingly, they are also demanded in regard to high frequency devices.
For example, in materials for the resonator, the following characteristics are required for the using frequency to improve and miniaturize characteristics of the high frequency characteristics.
(1) Specific dielectric constant is large: The resonator to be used nearly the microwave often utilizes that the wave length is shortened in a dielectric substance in proportion to the inverse number of a square root of dielectric constant. Accordingly, the length of the resonator can shorten the wavelength in proportion to the reverse number of the square root of the dielectric constant.
(2) Q is large: For the materials of the microwave, Q to be defined with Q=1/tan .delta. is used as valuation of dielectric loss, and that Q is large means the loss is small.
(3) Temperature change of the dielectric constant is small: The temperature change of the resonance frequency of the resonator or the filter is controlled to the utmost. Therefore, it is desirable that the temperature change of the dielectric constant is small.
(4) The sintering at low temperature is possible: It has recently been required to miniaturize electronic devices accompanying with miniaturization of the mobile communication instruments. Therefore, for realizing the miniaturization of devices, parts of surface mount devices (SMD) holding conductive electrodes within interiors thereof are changing to main streams. In this case, it is desirable to use Ag or Cu being low resistance as conductive electrodes for improving the loss characteristics of the device. However, since Ag or Cu has low melting points, it is required that the dielectric porcelain may be burned at temperature lower than their melting points. The matter of this concurrent burning is also pointed out when Ag or Cu is made capacitor materials for temperature compensation.
As the dielectric materials for the microwave, compositions as BaO.multidot.4TiO.sub.2 group or BaO.multidot.rare earth oxide.multidot.TiO.sub.2 group are known. In particular, as BaO.multidot.Nd.sub.2 O.sub.3.multidot.TiO.sub.2 group is high in the dielectric constant and the Q value, comprehensive studies have been made thereon. Recently, the sintering at low temperature has been carried out in these compositions, and is described in JP-A-3-295856, JP-A-5-97508, JP-A-6-223625, JP-A-6-211564, JP-A-5-234420, JP-A-5-319921, JP-A-5-319920, JP-A-6-116021, JP-A-6-116022, JP-A-8-167322, JP-A-8-167323, JP-A-8-208329, JP-A-8-167324, JP-A-8-208328, JP-A-5-319922, or JP-A-8-245262. (JP-A means "Unexamined Japanese Patent Publication (kokai))
In these technologies, BaO.multidot.rare earth oxide.multidot.TiO.sub.2 are used as a main component to which glass composition or glass composition and several kinds of sub component are added for carrying out the sintering at low temperature.
However, almost all of them contain PbO or Bi.sub.2 O.sub.3 in the main component or additives. Since PbO and Bi.sub.2 O.sub.3 also have promoting effects of the sintering at low temperature in addition to improvement of the characteristics such as increasing the dielectric constant, effects of both are utilized for practicing as the materials sintered at low temperature for high frequency.
As described above, the dielectric porcelain of BaO.multidot.Nd.sub.2 O.sub.3.multidot.TiO.sub.2 group is high in the dielectric constant and Q, and small in temperature coefficient of the dielectric constant. It is utilized for dielectric substance for microwave. The sintering at low temperature has recently been realized in BaO.multidot.Nd.sub.2 O.sub.3.multidot.TiO.sub.2 group, and PbO and Bi.sub.2 O.sub.3 are added for increasing the characteristics and promoting the sintering at low temperature. There are very scarcely inventions without both of PbO and Bi.sub.2 O.sub.3.
Environmental protection campaign of a global scale has further been raised. Therefore, also in the fields of electronic parts, it is expected to reduce environmental contaminating substances as PbO, Bi.sub.2 O.sub.3 and others. When substances contain environmental contamination, treating facilities of waste liquid or special equipment are necessary in manufacturing processes, and also in view of production cost, it is desirous not to contain such contaminating substances. Further, PbO, and Bi.sub.2 O.sub.3 are easily evaporated at high temperature, and ready for dispersing factors, and yet being neither PbO nor Bi.sub.2 O.sub.3 is desired.